A wind turbine known in the art comprises a wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with a number of wind turbine blades is connected to the nacelle through a low speed shaft, as illustrated on FIG. 1.
As modern wind turbines get bigger and bigger, both in size and in output, the demand for more efficient wind turbine components is increased. But as the components of, for example, the drive train of the wind turbine get bigger, it becomes increasingly difficult and costly to ensure the rigidity of the drive train.
Furthermore, large modern wind turbines—in particular turbines above 1 MW—have slow turning rotors and the rotation speed is generally lower the larger the rotor diameter is. This is in disfavour for the energy converting system.
On the current MW wind turbines most gearboxes have a planetary gear as a first stage and the following stages are either planetary or helical gears. The first stage planetary gears have most commonly 3 planets of relatively large diameter and a sun gear of a relatively small diameter.
An example of this is disclosed in PCT application no. WO 91/19916, wherein a main shaft of a wind turbine is provided with two main bearings and an epicyclical gearbox comprising at least two gear stages. One of the downsides of this drive train design is that to ensure that all the components are in their right place at all times, all components have to be rigidly fixed in relation to each other. This demands a rigid, heavy and expensive construction.
An object of the invention is to provide for a wind turbine with a drive train which is more cost and weight efficient.